Messages in this thread Patch in this message | | | From | Amit Shah <> | Subject | [PATCH] hvc_console: Fix a race between hvc_close and hvc_remove | Date | Fri, 26 Feb 2010 17:16:26 +0530 |
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Alan pointed out a race in the code where hvc_remove is invoked. The recent virtio_console work is the first user of hvc_remove().
Alan describes it thus:
The hvc_console assumes that a close and remove call can't occur at the same time.
In addition tty_hangup(tty) is problematic as tty_hangup is asynchronous itself....
So this can happen
hvc_close hvc_remove hung up ? - no lock tty = hp->tty unlock lock hp->tty = NULL unlock notify del kref_put the hvc struct close completes tty is destroyed tty_hangup dead tty tty->ops will be NULL NULL->...
This patch adds some tty krefs and also converts to using tty_vhangup() before putting the tty kref.
Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Amit Shah <amit.shah@redhat.com> CC: Alan Cox <alan@lxorguk.ukuu.org.uk> CC: linuxppc-dev@ozlabs.org CC: Rusty Russell <rusty@rustcorp.com.au> ---
I can't be sure if this is all that's needed. tty people, please take a look!
drivers/char/hvc_console.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index d8dac58..3983e32 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -106,6 +106,7 @@ static struct hvc_struct *hvc_get_by_index(int index) spin_lock_irqsave(&hp->lock, flags); if (hp->index == index) { kref_get(&hp->kref); + tty_kref_get(hp->tty); spin_unlock_irqrestore(&hp->lock, flags); spin_unlock(&hvc_structs_lock); return hp; @@ -390,6 +391,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) } kref_put(&hp->kref, destroy_hvc_struct); + tty_kref_put(tty); } static void hvc_hangup(struct tty_struct *tty) @@ -806,6 +808,7 @@ int hvc_remove(struct hvc_struct *hp) unsigned long flags; struct tty_struct *tty; + tty_kref_get(hp->tty); spin_lock_irqsave(&hp->lock, flags); tty = hp->tty; @@ -830,7 +833,9 @@ int hvc_remove(struct hvc_struct *hp) * cleaned up the hvc_struct. */ if (tty) - tty_hangup(tty); + tty_vhangup(tty); + + tty_kref_put(hp->tty); return 0; } EXPORT_SYMBOL_GPL(hvc_remove); -- 1.6.2.5
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